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Design and simulation of a ZnO microcantilever based vibration energy harvester

Author

Vivek Damodar, Ranjan

Date of Issue

2016

School

School of Mechanical and Aerospace Engineering

Abstract

In today’s world, piezoelectric materials find applications in almost every field of cutting edge technology including Microelectromechanical systems (MEMS). The applications of these microstructures are diverse and multidisciplinary, ranging from sensors, transducers etc., to power sources and energy harvesters. Until now, lead zirconate titanate (PZT) has been the predominant material used in MEMS based devices, owing to its high piezoelectric charge coefficient. However, because of the toxic nature of the lead contained in PZT, design and fabrication of alternative lead free materials, as an effective and efficient replacement is being widely researched. In this project, we study the feasibility of using one such alternative material i.e. zinc oxide (ZnO) making use of a composite microcantilever beam structure for MEMS based vibration energy harvesting application.
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Piezoelectric vibration energy harvesters rely on resonance to generate power, which in turn is dependent on the geometry of the beam and the frequency of the ambient vibrations. Hence, finite element method (FEM) simulations have been performed using COMSOL Multiphysics software to study the influence of the geometrical parameters of the beam on its first resonant frequency. A proof mass is introduced at the free end of the cantilever beam to bring down its first resonant frequency to the ambient range (100-200 Hz). Utilizing the results of the simulation, an optimized geometry for the microcantilever beam is proposed for further analysis. In addition, the variation in natural frequency of the cantilever beam on using different substrate and proof mass materials was analyzed. Next, a frequency response analysis is performed on the optimized geometry to determine the electric power output of the energy harvester, on applying a body load across a frequency domain close to the first Eigen frequency of the beam. Furthermore, the output voltage and electric power output generated by the beam is measured as a function of load resistance, at the resonance frequency keeping the acceleration constant.
Due to the miniaturization and highly complex nature of the structures involved in MEMS, 3D additive manufacturing technologies have recently been garnering attention for fabrication as opposed to conventional manufacturing techniques. Therefore, a few additive techniques have been studied and explored as part of this dissertation in the fabrication of the proposed multilayered
cantilever beam.